RFC 5353 Endpoint Handlespace Redundancy September 20081. Introduction
ENRP is designed to work in conjunction with ASAP [RFC5352] to
accomplish the functionality of RSerPool as defined by its
requirements [RFC3237].
Within the operational scope of RSerPool, ENRP defines the procedures
and message formats of a distributed, fault-tolerant registry service
for storing, bookkeeping, retrieving, and distributing pool operation
and membership information.
Whenever appropriate, in the rest of this document, we will refer to
this RSerPool registry service as ENRP handlespace, or simply
handlespace, because it manages all pool handles.
1.1. Definitions
This document uses the following terms:
Operational scope: The part of the network visible to pool users by
a specific instance of the reliable server pooling protocols.
Pool (or server pool): A collection of servers providing the same
application functionality.
Pool handle: A logical pointer to a pool. Each server pool will be
identifiable in the operational scope of the system by a unique
pool handle.
Pool element: A server entity having registered to a pool.
Pool user: A server pool user.
Pool element handle (or endpoint handle): A logical pointer to a
particular pool element in a pool, consisting of the pool handle
and a destination transport address of the pool element.
Handle space: A cohesive structure of pool handles and relations
that may be queried by an internal or external agent.
ENRP client channel: The communication channel through which an ASAP
User (either a Pool Element (PE) or Pool User (PU)) requests ENRP
handlespace service. The client channel is usually defined by the
transport address of the Home ENRP server and a well-known port
number.
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RFC 5353 Endpoint Handlespace Redundancy September 2008
ENRP server channel: Defined by a list of IP addresses (one for each
ENRP server in an operational scope) and a well-known port number.
All ENRP servers in an operational scope can send "group-cast"
messages to other servers through this channel. In a "group-
cast", the sending server sends multiple copies of the message,
one to each of its peer servers, over a set of point-to-point
Stream Control Transmission Protocol (SCTP) associations between
the sending server and the peers. The "group-cast" may be
conveniently implemented with the use of the "SCTP_SENDALL" option
on a one-to-many style SCTP socket.
Home ENRP server: The ENRP server to which a PE or PU currently
belongs. A PE MUST only have one Home ENRP server at any given
time, and both the PE and its Home ENRP server MUST keep track of
this master/slave relationship between them. A PU SHOULD select
one of the available ENRP servers as its Home ENRP server.
1.2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. ENRP Message Definitions
In this section, we define the format of all ENRP messages. These
are messages sent and received amongst ENRP servers in an operational
scope. Messages sent and received between a PE/PU and an ENRP server
are part of ASAP and are defined in [RFC5352]. A common format, that
is defined in [RFC5354], is used for all ENRP and ASAP messages.
Most ENRP messages contain a combination of fixed fields and TLV
(Type-Length-Value) parameters. The TLV parameters are also defined
in [RFC5354]. If a nested TLV parameter is not ended on a 32-bit
word boundary, it will be padded with all '0' octets to the next 32-
bit word boundary.
All messages, as well as their fields/parameters described below,
MUST be transmitted in network byte order (aka Big Endian, meaning
the most significant byte is transmitted first).
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Receiving Server's ID: 32 bits (unsigned integer)
This is the ID of the ENRP server to which this message is
intended. If the message is not intended for an individual
server (e.g., the message is group-casted to a group of
servers), this field MUST be sent with all 0s. If the message
is sent point-to-point, this field MAY be sent with all 0s.
PE Checksum Parameter:
This is a TLV that contains the latest PE checksum of the ENRP
server that sends the ENRP_PRESENCE. This parameter SHOULD be
included for handlespace consistency auditing. See
Section 3.6.1 for details.
Server Information Parameter:
If this parameter is present, it contains the server
information of the sender of this message (the Server
Information Parameter is defined in [RFC5354]). This parameter
is optional. However, if this message is sent in response to a
received "reply required" ENRP_PRESENCE from a peer, the sender
then MUST include its server information.
Note, at startup, an ENRP server MUST pick a randomly generated, non-
zero 32-bit unsigned integer as its ID and MUST use this same ID
until the ENRP server is rebooted.
2.2. ENRP_HANDLE_TABLE_REQUEST Message
An ENRP server sends this message to one of its peers to request a
copy of the handlespace data. This message is normally used during
server initialization or handlespace re-synchronization.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x02 |0|0|0|0|0|0|0|W| Message Length = 0xC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sending Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiving Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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R (Reject) Flag: 1 bit
MUST be set to '1' if the sender of this message is rejecting a
handlespace request. In this case, pool entries MUST NOT be
included. This might happen if the sender of this message is
in the middle of initializing its database or is under high
load.
Message Length: 16 bits (unsigned integer)
Indicates the entire length of the message, including the
header, in number of octets.
Note, the value in the Message Length field will NOT cover any
padding at the end of this message.
Sending Server's ID:
See Section 2.1.
Receiving Server's ID:
See Section 2.1.
Pool Entry #1-#n:
If the R flag is set to '0', at least one pool entry SHOULD be
present in this message. Each pool entry MUST start with a
Pool Handle parameter, as defined in Section 3.9 of [RFC5354],
and is followed by one or more Pool Element parameters in TLV
format, as shown below:
+---------------------------+
: Pool Handle :
+---------------------------+
: PE #1 :
+---------------------------+
: PE #2 :
+---------------------------+
: ... :
+---------------------------+
: PE #n :
+---------------------------+
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RFC 5353 Endpoint Handlespace Redundancy September 20083.1. Methods for Communicating amongst ENRP Servers
Within an RSerPool operational scope, ENRP servers need to
communicate with each other in order to exchange information, such as
the pool membership changes, handlespace data synchronization, etc.
Two types of communications are used amongst ENRP servers:
o point-to-point message exchanges from one ENPR server to a
specific peer server, and
o announcements from one server to all its peer servers in the
operational scope.
Point-to-point communication is always carried out over an SCTP
association between the sending server and the receiving server.
Announcements are sent out via "group-casts" over the ENRP server
channel.
3.2. ENRP Server Initialization
This section describes the steps a new ENRP server needs to take in
order to join the other existing ENRP servers, or to initiate the
handlespace service if it is the first ENRP server started in the
operational scope.
3.2.1. Generate a Server Identifier
A new ENRP server MUST generate a non-zero, 32-bit server ID that is
as unique as possible among all the ENRP servers in the operational
scope, and this server ID MUST remain unchanged for the lifetime of
the server. Normally, a good 32-bit random number will be good
enough, as the server ID [RFC4086] provides some information on
randomness guidelines.
Note, there is a very remote chance (about 1 in about 4 billion) that
two ENRP servers in an operational scope will generate the same
server ID and hence cause a server ID conflict in the pool. However,
no severe consequence of such a conflict has been identified.
Note, the ENRP server ID space is separate from the PE Id space
defined in [RFC5352].
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RFC 5353 Endpoint Handlespace Redundancy September 20083.2.2. Acquire Peer Server List
At startup, the ENRP server (the initiating server) will first
attempt to learn of all existing peer ENRP servers in the same
operational scope, or to determine that it is alone in the scope.
The initiating server uses an existing peer server to bootstrap
itself into service. We call this peer server the mentor server.
3.2.2.1. Finding the Mentor Server
If the initiating server is told about one existing peer server
through some administrative means (such as DNS query, configuration
database, startup scripts, etc.), the initiating server MUST then use
this peer server as its mentor server.
If multiple existing peer servers are specified, the initiating
server MUST pick one of them as its mentor server and keep the others
as its backup mentor servers.
If no existing peer server is specified, the initiating server MUST
assume that it is alone in the operational scope, and MUST skip the
procedures in Section 3.2.2.2 and Section 3.2.3 and MUST consider its
initialization completed and start offering ENRP services.
3.2.2.2. Request Complete Server List from Mentor Peer
Once the initiating server finds its mentor peer server (by either
discovery or administrative means), the initiating server MUST send
an ENRP_LIST_REQUEST message to the mentor peer server to request a
copy of the complete server list maintained by the mentor peer (see
Section 3.4 for maintaining a server list).
The initiating server SHOULD start a MAX-TIME-NO-RESPONSE timer every
time it finishes sending an ENRP_LIST_REQUEST message. If the timer
expires before receiving a response from the mentor peer, the
initiating server SHOULD abandon the interaction with the current
mentor server and send a new server list request to a backup mentor
peer, if one is available.
Upon the reception of this request, the mentor peer server SHOULD
reply with an ENRP_LIST_RESPONSE message and include in the message
body all existing ENRP servers known by the mentor peer.
Upon the reception of the ENRP_LIST_RESPONSE message from the mentor
peer, the initiating server MUST use the server information carried
in the message to initialize its own peer list.
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However, if the mentor itself is in the process of startup and not
ready to provide a peer server list (for example, the mentor peer is
waiting for a response to its own ENRP_LIST_REQUEST to another
server), it MUST reject the request by the initiating server and
respond with an ENRP_LIST_RESPONSE message with the R flag set to
'1', and with no server information included in the response.
In the case where its ENRP_LIST_REQUEST is rejected by the mentor
peer, the initiating server SHOULD either wait for a few seconds and
re-send the ENRP_LIST_REQUEST to the mentor server, or if there is a
backup mentor peer available, select another mentor peer server and
send the ENRP_LIST_REQUEST to the new mentor server.
3.2.3. Download ENRP Handlespace Data from Mentor Peer
After a peer list download is completed, the initiating server MUST
request a copy of the current handlespace data from its mentor peer
server, by taking the following steps:
1. The initiating server MUST first send an
ENRP_HANDLE_TABLE_REQUEST message to the mentor peer, with the W
flag set to '0', indicating that the entire handlespace is
requested.
2. Upon the reception of this message, the mentor peer MUST start a
download session in which a copy of the current handlespace data
maintained by the mentor peer is sent to the initiating server in
one or more ENRP_HANDLE_TABLE_RESPONSE messages. (Note, the
mentor server may find it particularly desirable to use multiple
ENRP_HANDLE_TABLE_RESPONSE messages to send the handlespace when
the handlespace is large, especially when forming and sending out
a single response containing a large handlespace may interrupt
its other services.)
If more than one ENRP_HANDLE_TABLE_RESPONSE message is used
during the download, the mentor peer MUST use the M flag in each
ENRP_HANDLE_TABLE_RESPONSE message to indicate whether this
message is the last one for the download session. In particular,
the mentor peer MUST set the M flag to '1' in the outbound
ENRP_HANDLE_TABLE_RESPONSE if there is more data to be
transferred and MUST keep track of the progress of the current
download session. The mentor peer MUST set the M flag to '0' in
the last ENRP_HANDLE_TABLE_RESPONSE for the download session and
close the download session (i.e., removing any internal record of
the session) after sending out the last message.
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3. During the downloading, every time the initiating server receives
an ENRP_HANDLE_TABLE_RESPONSE message, it MUST transfer the data
entries carried in the message into its local handlespace
database, and then check whether or not this message is the last
one for the download session.
If the M flag is set to '1' in the just processed
ENRP_HANDLE_TABLE_RESPONSE message, the initiating server MUST
send another ENRP_HANDLE_TABLE_REQUEST message to the mentor peer
to request for the next ENRP_HANDLE_TABLE_RESPONSE message.
4. When unpacking the data entries from a ENRP_HANDLE_TABLE_RESPONSE
message into its local handlespace database, the initiating
server MUST handle each pool entry carried in the message using
the following rules:
A. If the pool does not exist in the local handlespace, the
initiating server MUST create the pool in the local
handlespace and add the PE(s) in the pool entry to the pool.
When creating the pool, the initiation server MUST set the
overall member selection policy type of the pool to the
policy type indicated in the first PE.
B. If the pool already exists in the local handlespace, but the
PE(s) in the pool entry is not currently a member of the
pool, the initiating server MUST add the PE(s) to the pool.
C. If the pool already exists in the local handlespace AND the
PE(s) in the pool entry is already a member of the pool, the
initiating server SHOULD replace the attributes of the
existing PE(s) with the new information. ENRP will make sure
that the information stays up to date.
5. When the last ENRP_HANDLE_TABLE_RESPONSE message is received from
the mentor peer and unpacked into the local handlespace, the
initialization process is completed and the initiating server
SHOULD start to provide ENRP services.
Under certain circumstances, the mentor peer itself may not be able
to provide a handlespace download to the initiating server. For
example, the mentor peer is in the middle of initializing its own
handlespace database, or it currently has too many download sessions
open to other servers.
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In such a case, the mentor peer MUST reject the request by the
initiating server and respond with an ENRP_HANDLE_TABLE_RESPONSE
message with the R flag set to '1', and with no pool entries included
in the response.
In the case where its ENRP_HANDLE_TABLE_REQUEST is rejected by the
mentor peer, the initiating server SHOULD either wait for a few
seconds and re-send the ENRP_HANDLE_TABLE_REQUEST to the mentor
server, or if there is a backup mentor peer available, select another
mentor peer server and send the ENRP_HANDLE_TABLE_REQUEST to the new
mentor server.
A handlespace download session that has been started may get
interrupted for some reason. To cope with this, the initiating
server SHOULD start a timer every time it finishes sending an
ENRP_HANDLE_TABLE_REQUEST to its mentor peer. If this timer expires
without receiving a response from the mentor peer, the initiating
server SHOULD abort the current download session and re-start a new
handlespace download with a backup mentor peer, if one is available.
Similarly, after sending out an ENRP_HANDLE_TABLE_RESPONSE, and the
mentor peer setting the M-bit to '1' to indicate that it has more
data to send, it SHOULD start a session timer. If this timer expires
without receiving another request from the initiating server, the
mentor peer SHOULD abort the session, cleaning out any resource and
record of the session.
3.3. Server Handlespace Update
This includes a set of update operations used by an ENRP server to
inform its peers when its local handlespace is modified, e.g.,
addition of a new PE, removal of an existing PE, change of pool or PE
properties.
3.3.1. Announcing Additions or Updates of PE
When a new PE is granted registration to the handlespace or an
existing PE is granted a re-registration, the Home ENRP server uses
this procedure to inform all its peers.
This is an ENRP announcement and is sent to all the peer of the Home
ENRP server. See Section 3.1 on how announcements are sent.
An ENRP server MUST announce this update to all its peers in a
ENRP_HANDLE_UPDATE message with the Update Action field set to
'ADD_PE', indicating the addition of a new PE or the modification of
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an existing PE. The complete new information of the PE and the pool
it belongs to MUST be indicated in the message with a PE parameter
and a Pool Handle parameter, respectively.
The Home ENRP server SHOULD fill in its server ID in the Sending
Server's ID field and leave the Receiving Server's ID blank (i.e.,
all 0s).
When a peer receives this ENRP_HANDLE_UPDATE message, it MUST take
the following actions:
1. If the named pool indicated by the pool handle does not exist in
its local copy of the handlespace, the peer MUST create the named
pool in its local handlespace and add the PE to the pool as the
first PE. It MUST then copy in all other attributes of the PE
carried in the message.
When the new pool is created, the overall member selection policy
of the pool MUST be set to the policy type indicated by the PE.
2. If the named pool already exists in the peer's local copy of the
handlespace *and* the PE does not exist, the peer MUST add the PE
to the pool as a new PE and copy in all attributes of the PE
carried in the message.
3. If the named pool exists *and* the PE is already a member of the
pool, the peer MUST replace the attributes of the PE with the new
information carried in the message.
3.3.2. Announcing Removal of PE
When an existing PE is granted de-registration or is removed from its
handlespace for some other reasons (e.g., purging an unreachable PE,
see Section 3.5 in [RFC5352]), the ENRP server MUST use this
procedure to inform all its peers about the change just made.
This is an ENRP announcement and is sent to all the peers of the Home
ENRP server. See Section 3.1 on how announcements are sent.
An ENRP server MUST announce the PE removal to all its peers in an
ENRP_HANDLE_UPDATE message with the Update Action field set to
DEL_PE, indicating the removal of an existing PE. The complete
information of the PE and the pool it belongs to MUST be indicated in
the message with a PE parameter and a Pool Handle parameter,
respectively.
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The sending server MUST fill in its server ID in the Sending Server's
ID field and leave the Receiving Server's ID blank (i.e., set to all
0s).
When a peer receives this ENRP_HANDLE_UPDATE message, it MUST first
find the pool and the PE in its own handlespace, and then remove the
PE from its local handlespace. If the removed PE is the last one in
the pool, the peer MUST also delete the pool from its local
handlespace.
If the peer fails to find the PE or the pool in its handlespace, it
SHOULD take no further actions.
3.4. Maintaining Peer List and Monitoring Peer Status
An ENRP server MUST keep an internal record on the status of each of
its known peers. This record is referred to as the server's "peer
list".
3.4.1. Discovering New Peer
If a message of any type is received from a previously unknown peer,
the ENRP server MUST consider this peer a new peer in the operational
scope and add it to the peer list.
The ENRP server MUST send an ENRP_PRESENCE message with the Reply-
required flag set to '1' to the source address found in the arrived
message. This will force the new peer to reply with its own
ENRP_PRESENCE containing its full server information (see
Section 2.1).
3.4.2. Server Sending Heartbeat
Every PEER-HEARTBEAT-CYCLE seconds, an ENRP server MUST announce its
continued presence to all its peer with a ENRP_PRESENCE message. In
the ENRP_PRESENCE message, the ENRP server MUST set the
'Replay_required' flag to '0', indicating that no response is
required.
The arrival of this periodic ENRP_PRESENCE message will cause all its
peers to update their internal variable "peer_last_heard" for the
sending server (see Section 3.4.3 for more details).
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RFC 5353 Endpoint Handlespace Redundancy September 20083.4.3. Detecting Peer Server Failure
An ENRP server MUST keep an internal variable "peer_last_heard" for
each of its known peers and the value of this variable MUST be
updated to the current local time every time a message of any type
(point-to-point or announcement) is received from the corresponding
peer.
If a peer has not been heard for more than MAX-TIME-LAST-HEARD
seconds, the ENRP server MUST immediately send a point-to-point
ENRP_PRESENCE with the Reply_request flag set to '1' to that peer.
If the send fails or the peer does not reply after MAX-TIME-NO-
RESPONSE seconds, the ENRP server MUST consider the peer server dead
and SHOULD initiate the takeover procedure defined in Section 3.5.
3.5. Taking Over a Failed Peer Server
In the following descriptions, we call the ENRP server that detects
the failed peer server and initiates the takeover the "initiating
server" and the failed peer server the "target server". This allows
the PE to continue to operate in case of a failure of their Home ENRP
server.
3.5.1. Initiating Server Take-over Arbitration
The initiating server SHOULD first start the takeover arbitration
process by sending an ENRP_INIT_TAKEOVER message to all its peer
servers. See Section 3.1 on how announcements are sent. In the
message, the initiating server MUST fill in the Sending Server's ID
and Targeting Server's ID. The goal is that only one ENRP server
takes over the PE from the target.
After announcing the ENRP_INIT_TAKEOVER message ("group-casting" to
all known peers, including the target server), the initiating server
SHOULD wait for an ENRP_INIT_TAKEOVER_ACK message from each of its
known peers, except that of the target server.
Each peer receiving an ENRP_INIT_TAKEOVER message from the initiating
server MUST take the following actions:
1. If the peer server determines that it (itself) is the target
server indicated in the ENRP_INIT_TAKEOVER message, it MUST
immediately announce an ENRP_PRESENCE message to all its peer
ENRP servers in an attempt to stop this takeover process. This
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RFC 5353 Endpoint Handlespace Redundancy September 2008
indicates a false failure-detection case by the initiating
server. The initiating server MUST stop the takeover operation
by marking the target server as "active" and taking no further
takeover actions.
2. If the peer server finds that it has already started its own
takeover arbitration process on the same target server, it MUST
perform the following arbitration:
A. If the peer's server ID is smaller in value than the Sending
Server's ID in the arrived ENRP_INIT_TAKEOVER message, the
peer server MUST immediately abort its own take-over attempt
by taking no further takeover actions of its own. Moreover,
the peer MUST mark the target server as "not active" on its
internal peer list so that its status will no longer be
monitored by the peer, and reply to the initiating server
with an ENRP_INIT_TAKEOVER_ACK message.
B. Otherwise, the peer MUST ignore the ENRP_INIT_TAKEOVER
message.
3. If the peer finds that it is neither the target server nor is in
its own takeover process, the peer MUST: a) mark the target
server as "not active" on its internal peer list so that its
status will no longer be monitored by this peer, and b) MUST
reply to the initiating server with an ENRP_INIT_TAKEOVER_ACK
message.
Once the initiating server has received the ENRP_INIT_TAKEOVER_ACK
message from all of its currently known peers (except for the target
server), it MUST consider that it has won the arbitration and MUST
proceed to complete the takeover, following the steps described in
Section 3.5.2.
However, if it receives an ENRP_PRESENCE from the target server at
any point in the arbitration process, the initiating server MUST
immediately stop the takeover process and mark the status of the
target server as "active".
3.5.2. Takeover Target Peer Server
The initiating ENRP server MUST first send, via an announcement, an
ENRP_TAKEOVER_SERVER message to inform all its active peers that the
takeover has been enforced. The target server's ID MUST be filled in
the message. The initiating server SHOULD then remove the target
server from its internal peer list.
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RFC 5353 Endpoint Handlespace Redundancy September 2008
Then, it SHOULD examine its local copy of the handlespace and claim
ownership of each of the PEs originally owned by the target server,
by following these steps:
1. mark itself as the Home ENRP server of each of the PEs originally
owned by the target server;
2. send a point-to-point ASAP_ENDPOINT_KEEP_ALIVE message, with the
'H' flag set to '1', to each of the PEs. This will trigger the
PE to adopt the initiating sever as its new Home ENRP server.
When a peer receives the ENRP_TAKEOVER_SERVER message from the
initiating server, it SHOULD update its local peer list and PE cache
by following these steps:
1. remove the target server from its internal peer list;
2. update the Home ENRP server of each PE in its local copy of the
handlespace to be the sender of the message, i.e., the initiating
server.
3.6. Handlespace Data Auditing and Re-synchronization
Message losses or certain temporary breaks in network connectivity
may result in data inconsistency in the local handlespace copy of
some of the ENRP servers in an operational scope. Therefore, each
ENRP server in the operational scope SHOULD periodically verify that
its local copy of handlespace data is still in sync with that of its
peers.
This section defines the auditing and re-synchronization procedures
for an ENRP server to maintain its handlespace data consistency.
3.6.1. Auditing Procedures
A checksum covering the data that should be the same is exchanged to
figure out whether or not the data is the same.
The auditing of handlespace consistency is based on the following
procedures:
1. An ENRP server SHOULD keep a separate PE checksum (a 16-bit
integer internal variable) for each of its known peers and for
itself. For an ENRP server with 'k' known peers, we denote these
internal variables as "pe_checksum_pr0", "pe_checksum_pr1", ...,
"pe_checksum_prk", where "pe_checksum_pr0" is the server's own PE
checksum. The list of what these checksums cover and a detailed
algorithm for calculating them is given in Section 3.6.2.
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RFC 5353 Endpoint Handlespace Redundancy September 2008
2. Each time an ENRP server sends out an ENRP_PRESENCE, it MUST
include in the message its current PE checksum (i.e.,
"pe_checksum_pr0").
3. When an ENRP server (server A) receives a PE checksum (carried in
an arrived ENRP_PRESENCE) from a peer ENRP server (server B),
server A SHOULD compare the PE checksum found in the
ENRP_PRESENCE with its own internal PE checksum of server B
(i.e., "pe_checksum_prB").
4. If the two values match, server A will consider that there is no
handlespace inconsistency between itself and server B, and it
should take no further actions.
5. If the two values do NOT match, server A SHOULD consider that
there is a handlespace inconsistency between itself and server B,
and a re-synchronization process SHOULD be carried out
immediately with server B (see Section 3.6.3).
3.6.2. PE Checksum Calculation Algorithm
When an ENRP server (server A) calculates an internal PE checksum for
a peer (server B), it MUST use the following algorithm.
Let us assume that in server A's internal handlespace, there are
currently 'M' PEs that are owned by server B. Each of the 'M' PEs
will then contribute to the checksum calculation with the following
byte block:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool handle string of the pool the PE belongs (padded with :
: zeros to next 32-bit word boundary, if needed) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PE Id (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note, these are not TLVs. This byte block gives each PE a unique
byte pattern in the scope. The 16-bit PE checksum for server B
"pe_checksum_prB" is then calculated over the byte blocks contributed
by the 'M' PEs one by one. The PE checksum calculation MUST use the
Internet algorithm described in [RFC1071].
Server A MUST calculate its own PE checksum (i.e., "pe_checksum_pr0")
in the same fashion, using the byte blocks of all the PEs owned by
itself.
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RFC 5353 Endpoint Handlespace Redundancy September 2008
Note, whenever an ENRP finds that its internal handlespace has
changed (e.g., due to PE registration/de-registration, receiving peer
updates, removing failed PEs, downloading handlespace pieces from a
peer, etc.), it MUST immediately update all its internal PE checksums
that are affected by the change.
Implementation Note: when the internal handlespace changes (e.g., a
new PE added or an existing PE removed), an implementation need not
re-calculate the affected PE checksum; it can instead simply update
the checksum by adding or subtracting the byte block of the
corresponding PE from the previous checksum value.
3.6.3. Re-Synchronization Procedures
If an ENRP server determines that there is inconsistency between its
local handlespace data and a peer's handlespace data with regard to
the PEs owned by that peer, it MUST perform the following steps to
re-synchronize the data:
1. The ENRP server SHOULD first "mark" every PE it knows about that
is owned by the peer in its local handlespace database;
2. The ENRP server SHOULD then send an ENRP_HANDLE_TABLE_REQUEST
message with the W flag set to '1' to the peer to request a
complete list of PEs owned by the peer;
3. Upon reception of the ENRP_HANDLE_TABLE_REQUEST message with the
W flag set to '1', the peer server SHOULD immediately respond
with an ENRP_HANDLE_TABLE_RESPONSE message listing all PEs
currently owned by the peer.
4. Upon reception of the ENRP_HANDLE_TABLE_RESPONSE message, the
ENRP server SHOULD transfer the PE entries carried in the message
into its local handlespace database. If a PE entry being
transferred already exists in its local database, the ENRP server
MUST replace the entry with the copy found in the message and
remove the "mark" from the entry.
5. After transferring all the PE entries from the received
ENRP_HANDLE_TABLE_RESPONSE message into its local database, the
ENRP server SHOULD check whether there are still PE entries that
remain "marked" in its local handlespace. If so, the ENRP server
SHOULD silently remove those "marked" entries.
Note, similar to what is described in Section 3.2.3, the peer may
reject the ENRP_HANDLE_TABLE_REQUEST or use more than one
ENRP_HANDLE_TABLE_RESPONSE message to respond.
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RFC 5353 Endpoint Handlespace Redundancy September 20083.7. Handling Unrecognized Messages or Unrecognized Parameters
When an ENRP server receives an ENRP message with an unknown message
type or a message of known type that contains an unknown parameter,
it SHOULD handle the unknown message or the unknown parameter
according to the unrecognized message and parameter handling rules
defined in Sections 3 and 4 in [RFC5354].
According to the rules, if an error report to the message sender is
needed, the ENRP server that discovered the error SHOULD send back an
ENRP_ERROR message with a proper error cause code.
4. Variables and Thresholds4.1. Variables
peer_last_heard - The local time that a peer server was last heard
(via receiving either a group-cast or point-to-point message from
the peer).
pe_checksum_pr - The internal 16-bit PE checksum that an ENRP server
keeps for a peer. A separate PE checksum is kept for each of its
known peers as well as for itself.
4.2. Thresholds
PEER-HEARTBEAT-CYCLE - The period for an ENRP server to announce a
heartbeat message to all its known peers. (Default=30 secs.)
MAX-TIME-LAST-HEARD - Pre-set threshold for how long an ENRP server
will wait before considering a silent peer server potentially
dead. (Default=61 secs.)
MAX-TIME-NO-RESPONSE - Pre-set threshold for how long a message
sender will wait for a response after sending out a message.
(Default=5 secs.)
5. IANA Considerations
This document (RFC 5353) is the reference for all registrations
described in this section. All registrations have been listed on the
RSerPool Parameters page.
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RFC 5353 Endpoint Handlespace Redundancy September 20085.3. Port Numbers
The references for the already assigned port numbers
enrp-udp 9901/udp
enrp-sctp 9901/sctp
enrp-sctp-tls 9902/sctp
have been updated to RFC 5353.
5.4. SCTP Payload Protocol Identifier
The reference for the already assigned ENRP payload protocol
identifier 12 have been updated to RFC 5353.
6. Security Considerations
We present a summary of the threats to the RSerPool architecture and
describe security requirements in response to mitigate the threats.
Next, we present the security mechanisms, based on TLS, that are
implementation requirements in response to the threats. Finally, we
present a chain-of-trust argument that examines critical data paths
in RSerPool and shows how these paths are protected by the TLS
implementation.
6.1. Summary of RSerPool Security Threats
"Threats Introduced by Reliable Server Pooling (RSerPool) and
Requirements for Security in Response to Threats" [RFC5355] describes
the threats to the RSerPool architecture in detail and lists the
security requirements in response to each threat. From the threats
described in this document, the security services required for the
RSerPool protocol are enumerated below.
Threat 1) PE registration/de-registration flooding or spoofing
-----------
Security mechanism in response: ENRP server authenticates the PE.
Threat 2) PE registers with a malicious ENRP server
-----------
Security mechanism in response: PE authenticates the ENRP server.
Threats 1 and 2, taken together, result in mutual authentication of
the ENRP server and the PE.
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RFC 5353 Endpoint Handlespace Redundancy September 20086.2. Implementing Security Mechanisms
We do not define any new security mechanisms specifically for
responding to threats 1-7. Rather, we use an existing IETF security
protocol, specifically [RFC3237], to provide the security services
required. TLS supports all these requirements and MUST be
implemented. The TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite MUST be
supported, at a minimum, by implementers of TLS for RSerPool. For
purposes of backwards compatibility, ENRP SHOULD support
TLS_RSA_WITH_3DES_EDE_CBC_SHA. Implementers MAY also support any
other IETF-approved ciphersuites.
ENRP servers, PEs, and PUs MUST implement TLS. ENRP servers and PEs
MUST support mutual authentication using PSK. ENRP servers MUST
support mutual authentication among themselves using PSK. PUs MUST
authenticate ENRP servers using certificates.
TLS with PSK is mandatory to implement as the authentication
mechanism for ENRP to ENRP authentication and PE to ENRP
authentication. For PSK, having a pre-shared-key constitutes
authorization. The network administrators of a pool need to decide
which nodes are authorized to participate in the pool. The
justification for PSK is that we assume that one administrative
domain will control and manage the server pool. This allows for PSK
to be implemented and managed by a central security administrator.
TLS with certificates is mandatory to implement as the authentication
mechanism for PUs to the ENRP server. PUs MUST authenticate ENRP
servers using certificates. ENRP servers MUST possess a site
certificate whose subject corresponds to their canonical hostname.
PUs MAY have certificates of their own for mutual authentication with
TLS, but no provisions are set forth in this document for their use.
All RSerPool elements that support TLS MUST have a mechanism for
validating certificates received during TLS negotiation; this entails
possession of one or more root certificates issued by certificate
authorities (preferably, well-known distributors of site certificates
comparable to those that issue root certificates for web browsers).
In order to prevent man-in-the-middle attacks, the client MUST verify
the server's identity (as presented in the server's Certificate
message). The client's understanding of the server's identity
(typically the identity used to establish the transport connection)
is called the "reference identity". The client determines the type
(e.g., DNS name or IP address) of the reference identity and performs
a comparison between the reference identity and each subjectAltName
value of the corresponding type until a match is produced. Once a
match is produced, the server's identity has been verified, and the
server identity check is complete. Different subjectAltName types
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RFC 5353 Endpoint Handlespace Redundancy September 2008
are matched in different ways. The client may map the reference
identity to a different type prior to performing a comparison.
Mappings may be performed for all available subjectAltName types to
which the reference identity can be mapped; however, the reference
identity should only be mapped to types for which the mapping is
either inherently secure (e.g., extracting the DNS name from a URI to
compare with a subjectAltName of type dNSName) or for which the
mapping is performed in a secure manner (e.g., using DNS Security
(DNSSEC), or using user- or admin-configured host-to-address/
address-to-host lookup tables).
If the server identity check fails, user-oriented clients SHOULD
either notify the user or close the transport connection and indicate
that the server's identity is suspect. Automated clients SHOULD
close the transport connection and then return or log an error
indicating that the server's identity is suspect, or both. Beyond
the server identity check described in this section, clients should
be prepared to do further checking to ensure that the server is
authorized to provide the service it is requested to provide. The
client may need to make use of local policy information in making
this determination.
If the reference identity is an internationalized domain name,
conforming implementations MUST convert it to the ASCII Compatible
Encoding (ACE) format, as specified in Section 4 of [RFC3490], before
comparison with subjectAltName values of type dNSName. Specifically,
conforming implementations MUST perform the conversion operation
specified in Section 4 of [RFC3490] as follows: * in step 1, the
domain name SHALL be considered a "stored string"; * in step 3, set
the flag called "UseSTD3ASCIIRules"; * in step 4, process each label
with the "ToASCII" operation; and * in step 5, change all label
separators to U+002E (full stop).
After performing the "to-ASCII" conversion, the DNS labels and names
MUST be compared for equality according to the rules specified in
Section 3 of RFC 3490. The '*' (ASCII 42) wildcard character is
allowed in subjectAltName values of type dNSName, and then, only as
the left-most (least significant) DNS label in that value. This
wildcard matches any left-most DNS label in the server name. That
is, the subject *.example.com matches the server names a.example.com
and b.example.com, but does not match example.com or a.b.example.com.
When the reference identity is an IP address, the identity MUST be
converted to the "network byte order" octet string representation RFC791 [RFC0791] and RFC 2460 [RFC2460]. For IP version 4, as specified
in RFC 791, the octet string will contain exactly four octets. For
IP version 6, as specified in RFC 2460, the octet string will contain
exactly sixteen octets. This octet string is then compared against
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RFC 5353 Endpoint Handlespace Redundancy September 2008
subjectAltName values of type iPAddress. A match occurs if the
reference identity octet string and value octet strings are
identical.
After a TLS layer is established in a session, both parties are to
independently decide whether or not to continue based on local policy
and the security level achieved. If either party decides that the
security level is inadequate for it to continue, it SHOULD remove the
TLS layer immediately after the TLS (re)negotiation has completed
(see RFC 4511)[RFC4511]. Implementations may re-evaluate the
security level at any time and, upon finding it inadequate, should
remove the TLS layer.
Implementations MUST support TLS with SCTP, as described in [RFC3436]
or TLS over TCP, as described in [RFC5246]. When using TLS/SCTP we
must ensure that RSerPool does not use any features of SCTP that are
not available to a TLS/SCTP user. This is not a difficult technical
problem, but simply a requirement. When describing an API of the
RSerPool lower layer, we also have to take into account the
differences between TLS and SCTP.
Threat 8 requires the ASAP protocol to limit the number of
ASAP_ENDPOINT_UNREACHABLE messages (see Section 3.5 of RFC 5352) to
the ENRP server.
Threat 9 requires the ENRP protocol to limit the number of
ASAP_ENDPOINT_KEEP_ALIVE messages from the ENRP server to the PE.
There is no security mechanism defined for the multicast
announcements. Therefore, a receiver of such an announcement cannot
consider the source address of such a message to be a trustworthy
address of an ENRP server. A receiver must also be prepared to
receive a large number of multicast announcements from attackers.
6.3. Chain of Trust
Security is mandatory to implement in RSerPool and is based on TLS
implementation in all three architecture components that comprise
RSerPool -- namely PU, PE, and the ENRP server. We define an ENRP
server that uses TLS for all communication and authenticates ENRP
peers and PE registrants to be a secured ENRP server.
Here is a description of all possible data paths and a description of
the security.
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RFC 5353 Endpoint Handlespace Redundancy September 2008
PU <---> secured ENRP server (authentication of ENRP server;
queries over TLS)
PE <---> secured ENRP server (mutual authentication;
registration/de-registration over TLS)
secured ENRP server <---> secured ENRP server (mutual authentication;
database updates using TLS)
If all components of the system authenticate and communicate using
TLS, the chain of trust is sound. The root of the trust chain is the
ENRP server. If that is secured using TLS, then security will be
enforced for all ENRP and PE components that try to connect to it.
Summary of interaction between secured and unsecured components: If
the PE does not use TLS and tries to register with a secure ENRP
server, it will receive an error message response indicated as an
error due to security considerations and the registration will be
rejected. If an ENRP server that does not use TLS tries to update
the database of a secure ENRP server, then the update will be
rejected. If a PU does not use TLS and communicates with a secure
ENRP server, it will get a response with the understanding that the
response is not secure, as the response can be tampered with in
transit even if the ENRP database is secured.
The final case is the PU sending a secure request to ENRP. It might
be that ENRP and PEs are not secured and this is an allowable
configuration. The intent is to secure the communication over the
Internet between the PU and the ENRP server.
Summary:
RSerPool architecture components can communicate with each other to
establish a chain of trust. Secured PE and ENRP servers reject any
communications with unsecured ENRP or PE servers.
If the above is enforced, then a chain of trust is established for
the RSerPool user.
7. Acknowledgments
The authors wish to thank John Loughney, Lyndon Ong, Walter Johnson,
Thomas Dreibholz, Frank Volkmer, and many others for their invaluable
comments and feedback.
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RFC 5353 Endpoint Handlespace Redundancy September 2008
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Xie, et al. Experimental [Page 39]